Moorabi (Mammoth boss) -- You can let him turn into a mammoth and still get the acheivement this is how...
You need a player who can drop combat, aka rogue.
Kill him as usual stop dps at ~5%
Have the tank kite him up the ramp leaving to the entrance, rogue stays at the point where the moorabi encounter started by his altar
now the tank needs to autoattack the boss to 1-2%, rogue vanishes
Now everyone else in the party needs to be close to the tank, healer stops healing and everyone dies, at this point Moorabi resets, he turns into Human form and runs back to his altar at 1-2% hp, the rogue waits for him at the altar the and spams their attack right as he gets back this will re-encounter him b4 he goes back to 100% giving everyone the achievement.
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Snake boss, kite him to the entrance all the dps and healers stay in the water tank stays on the ramp, snakes cant swim and as long as the tank doesnt touch the adds they will all evade bug on the healer, this allows everyone to avoid snake wrap.